Clinical assessment of atlantoaxial instability using the Sharp-Purser test.

Anterior atlantoaxial subluxation is common in rheumatoid arthritis patients with involvement of the cervical spine. Sharp and Purser have described a test for the clinical assessment of this instability. We assessed the validity of the Sharp-Purser test in 123 outpatients with rheumatoid arthritis. Our findings indicate a predictive value of 85% and a specificity of 96%. The sensitivity was 88% when subluxation was greater than 4 mm. Our results show that the Sharp-Purser test is a useful clinical examination to diagnose atlantoaxial instability.